But then you walk out into Dealey Plaza and talk to the sidewalk conspiracy buffs, and you buy one of their pamphlets and go over to the grassy knoll and sit down and read it, and before long you begin to wonder if Oswald was even in Dallas that day.

People the world over make the pilgrimage to Dealey Plaza in search of answers, or some sense of closure, and most go home with neither. As the nation marks the 40th anniversary this week, the assassination of John F. Kennedy remains for many of us a disturbing mystery, a still-purple bruise on the national psyche.

But still we are drawn to Dallas. We come to gaze at the sniper's perch, hidden behind a wall of children's schoolbooks; to stand on the very spot where Abraham Zapruder shot history's most notorious home movie; to poke through the shrubs for clues that somehow eluded the thousands of searchers before us.

Driven by a morbid obsession, some are compelled to visit every site associated with the assassination, no matter how trivial: the former location of Jack Ruby's strip club, the Texas Theater, the street where Officer J. D. Tippit was gunned down, Oswald's quasi-secret gravesite.

Not long ago, one of those obsessives was me.

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I quickly got the impression that this is not Dallas' favorite topic of conversation. In Dealey Plaza, I had to search hard to find any official acknowledgement of what happened 40 years ago. Next to the grassy knoll there's a plaque -- to John Neely Byron, who founded a trading post on the site in 1839. On the former Texas School Book Depository, a big, wordy sign from the Texas Historical Commission covers in detail the site's various owners and uses through the years -- noting, among other things, that it once housed the offices of a plow-making company -- until finally, in the last sentence, it gets around to mentioning the assassination.

"Dallas hoped it had put all this behind it in the 1980s," said Jeff West, executive director of the Sixth Floor Museum at Dealey Plaza. "We had America's Team, and a wonderfully trashy TV show about us." In short, Dallas hoped the rest of the country would obsess about who shot JR, rather than who shot JFK.

Not much chance of that. In Dealey Plaza, someone for years has been painting a big X in the center lane on Elm Street as it slopes down toward the Triple Underpass: It purports to mark the exact spot where Kennedy was struck by the fatal bullet. This is just about the only fact in the case with which the majority of conspiracy buffs and lone-gunman advocates agree. And it's slightly wrong.

The X is, according to the Dallas Morning News, the work of 57-year-old Robert Groden, one of several men who regularly hawk conspiracy pamphlets in Dealey Plaza. The problem is that the lanes have been re-striped since 1963, and the X is actually about 6 inches too far to the west.

"If it is off," Groden conceded, "it's not off by much."

Nearly every day of the year, Groden and other conspiracy buffs man card tables around the plaza, pointing out suspicious (and bogus) bullet marks in the pavement and expounding on theories ranging from plausible to laughable. A few appear to be true believers; many are merely pitchmen for $5 brochures. When I pointed out to one hawker, 35-year-old Jimmy Longoria, that he hadn't even been born when Kennedy was shot, he drawled, "I wasn't around when Jesus was alive, either. But I still go to church."

In Dealey Plaza, I met people from all over the globe: a woman from Bangalore, India, in a sari, a group of visiting Israeli schoolteachers, a youth soccer team from Portugal. Richard Kangethe, a 57-year-old coffee farmer from Kenya, told me: "I'll never forget hearing about it over the radio in my village. I just had to come here." Ed Donahue and Brid Sharkey, both 26, from Dublin, said: "Being Irish, we grew up with JFK. He was one of us, the symbol of the Irish immigrant dream."

Behind the grassy knoll is a 4-foot-high picket fence separating the plaza from a railroad yard, and it was from behind this fence that most conspiracy theorists believe a second gunman fired. The back side of the fence has become a little shrine, covered with notes and plastic flowers and graffiti. "The shot was from here," scrawled someone named Jean, age 62. "I didn't know you, but I hope you're in heaven," wrote Kimberly Davis, a third- grader from Memphis Tennessee.

View from the window

It took Dallas until 1989 to open a museum dedicated to the assassination, but the Sixth Floor Museum at Dealey Plaza is exceedingly well done. You ride an elevator up to the sixth floor of the old book depository and are instantly transported back to 1963. The walls are hung with posters for the Broadway play Camelot; Chubby Checker's "The Twist" plays over your headphones; a television monitor shows clips from the Dick Van Dyke Show.

Soon the focus shifts to Kennedy. There's the menu for a White House dinner at which Pablo Casals played (and at which Inglenook Pinot Chardonnay and Almaden Cabernet Sauvignon were poured). Exhibits cover his economic and social programs, and the increasing turmoil of his presidency: Mafia prosecutions, civil rights marches, the Cuban missile crisis, Vietnam. Video screens show snippets of speeches, and I was struck anew by how witty and charismatic he was.

All the while, as I wound around the panels and displays, I could feel a palpable sense of dread growing. I was being led inexorably to the window at the southeast corner of the building. There, behind glass, the museum has re- created the sniper's nest, just as investigators discovered it. Cartons of school books are stacked to create a concealing wall, and others form the brace where Oswald steadied his mail-order Mannlicher-Carcano rifle.

You can't peer out that window (although you can get a real-time peek over the Internet by visiting www.jfk.org; click on EarthCam's Dealey Plaza Cam), but you get a very similar view from the adjoining window.

I spent more than half an hour there, tracing the route of the presidential motorcade as it came slowly down Houston Street, directly toward the sniper's perch - I'm not the only one who wondered why Oswald didn't take his shot then - and then slowed even further to make the hard left onto Elm. Just as Nellie Connally, wife of the Texas governor, finished saying to Kennedy, "You can't say Dallas doesn't love you, Mr. President," Oswald would have pulled the trigger.

The branches of the big oak tree that are thought to have deflected that bullet still hang over the street. I could see the spot where the second bullet struck Kennedy in the throat, and I could clearly make out the X that (almost) marks the location of the third and fatal shot. It was easy to picture Oswald standing up in his sniper's nest, a satisfied look on his face.

The following day, after touring nearly every Oswald-related site in Dallas with local historian Ken Holmes, I found myself standing over the assassin's grave in the Rose Hill Memorial Burial Park outside Fort Worth.

"The reporters who covered his burial had to act as pallbearers," Holmes said. "There was no one else around to do it."

There's a flat plaque on the ground engraved with "Oswald" and nothing else. For years, cemetery officials have refused to direct visitors to the site. (Directions are not hard to find, though, on the Internet.) But in a macabre bit of weirdness, there's a matching plaque on the adjacent grave engraved with "Nick Beef," the stage name of a local comic (who, apparently, is still alive). In his act, he told his audience that if they wanted to find Oswald's grave, all they had to do was ask cemetery workers to steer them to Nick Beef's site. That's not the only ghoulish aspect to the site. In 1981, Oswald's remains were exhumed after a British author made an apparently convincing case that the body in the grave was actually that of a Russian KGB agent who had impersonated Oswald. A team of pathologists at Baylor University examined dental records and concluded that the corpse was indeed Oswald's. It was reburied.

Whopper of a conspiracy

Nevertheless, I needed to give the conspiracy crowd its due. To do so, I knew, would send me down a rabbit hole into the shadowy world of poison darts, empty caskets, KGB impostors, forged autopsies, Corsican hit men and gunmen hiding in storm drains. And a whole cast of near-mythic characters: Umbrella Man, Babushka Lady, Badge Man, Frenchy, Black Dog Man, the Three Tramps and others.

Which is not to say this thinking is entirely outside the mainstream. Polls have consistently found that a majority of Americans believe a conspiracy was behind JFK's assassination. According to an exhibit at the Sixth Floor Museum, even Lyndon Johnson, who appointed the Warren Commission and officially accepted its findings, never believed Oswald was the lone gunman.

The problem with the conspiracy crowd is that there's no solid line between those who investigate clear and troubling lapses in the Warren Commission report and those who regularly share a Whopper with Elvis at Burger King.

Case in point: The Conspiracy Museum, located a block from Dealey Plaza. It's not merely about the JFK assassination; it sets forth what might be called the Grand Unifying Theory of conspiracy, linking Kennedy's death to those of his brother Robert and the Rev. Martin Luther King, plus Chappaquiddick (Ted Kennedy was supposedly the intended target) and -- I'm still scratching my head over this one -- the downing of Korean Airlines flight 007. Down in the basement, a sprawling, Asian-style mural somehow tries to tie it all together with imagery of cherry blossoms, birds and other symbols ... well, I didn't hang around long enough to sort it out. It was too weird and creepy.

On my way out, I paused to read a bulletin board full of newspaper clippings about the crash of the space shuttle Columbia, with various sentences double-underlined. The young man from the front counter hurried over. He had been watching me on the security monitors.

"We're not saying that this had anything to do with the other conspiracy, " he told me.

"Then why put it up?"

"We just found it ... " he raised an eyebrow "... interesting."

'It was absolute chaos'

Key figures in the case are regularly dying off, succumbing to old age, but it's still possible to speak with people who were there that day, who saw it with their own eyes.

Ann Atterberry was a 26-year-old reporter for the "women's page" at the Dallas Morning News. She wasn't assigned to cover the presidential visit, so she bought a sandwich in the paper's cafeteria and joined three friends to watch the lunchtime motorcade.

"It was really Jackie we wanted to see," she told me. "We wanted to get past the big crowds, so we went down to Dealey Plaza and sat on the curb and ate our lunches."

Atterberry walked me over to the spot, just east of the grassy knoll. She recalled how the motorcade turned sharply onto Elm and crept down the hill, passing within 10 feet of her. "I thought (Jackie) looked great in her pink pillbox hat. The sun was out, and her pink suit radiated. She was not terribly older than we were."

This was the end of the parade. In just a few seconds the motorcade would pass under the Triple Underpass and speed off to a luncheon at the Dallas Trade Mart.

"Jack and Jackie both looked pleased, and relieved," Atterberry said. "As they passed by us they waved, and they both made eye contact with us."

Tears moistened her eyes, and her voice cracked.

"I've often wondered if the four of us were the last thing he ever saw."

At almost the same instant, she heard the first crack of gunfire. "My first reaction was that it was a firecracker," she said. "I thought that was awfully rude. I was just turning to see where the sound came from when I heard the second shot. Just as I realized what it was, I heard the third shot, and then there was no doubt in my mind. We all burst into tears.

"It was absolute chaos. People on the knoll threw themselves on the ground. A motorcycle fell over and was left in the middle of the street. People were running everywhere."

Atterberry had been standing about 100 feet from Zapruder, and I asked her if she was in the famous home movie. She said she could never bring herself to look at it. (Later I watched the film in slow motion; there are four young women just where she said she and her friends were.)

"It's haunted me ever since," she said. "My roommate, one of the girls I was with that day, joined Kennedy's Peace Corps not long after that. Her psychologist told her she was doing this to atone, and she said no, but of course she was."

And maybe a similar instinct is what brings the rest of us to Dealey Plaza.

IF YOU GO

GETTING THERE

Dallas-Fort Worth Airport is a major hub with many nonstop flights each day from the Bay Area.

WHERE TO STAY

Amerisuites, Dallas West End, 1907 N. Lamar St., Dallas, TX 75202; (214) 999-0500; www.amerisuites.com/hotels/ajdw.shtml. Five-minute walk from Dealey Plaza; surprisingly nice for the price, with large rooms (although it's a stretch to call them suites), mini-refrigerators and microwaves. Using an online hotel discounter, I paid $65.95 a night, which included a breakfast buffet. For other options in all price ranges, contact the Convention and Visitors Bureau (see below).

WHAT TO DO

History tour, Frank Wilson, (214) 421-4500, Ext. 105, frank@dallashistory. org, www.dallashistory.org. The tour I took, "In the Steps of Lee Harvey Oswald," is offered twice a year through the Dallas Historical Society. The fall tour was Nov. 15; the next will be in April 2004. Cost is $45. Groups can arrange a private tour at other times. The price varies; I paid $135, which covered four people.